Devices and Probes for Intracavitary pH Monitoring

The majority of diseases of the upper segments of the gastrointestinal tract (GIT) correlate with the effect of the acid produced during digestion on the mucous coat of the GIT. Correct diagnosis of these diseases requires examination of the acidogenic antacid functions of the GIT. Investigation of the acidogenic function of the stomach began as early as 1824. Until recently, aspiration of the gastric content with further measurement of its acidity (by titration or electrometry) was the main acidometric method used in medical practice. However, in the 1940s it became evident that the accuracy and the information value of this method were rather low. Besides, the aspiration procedure is rather painful and stressful for GIT tissues, which has an effect on the results of measurement.

McClendon was the first to suggest a pH measuring probe with a calomel reference electrode for measuring intragastric acidity. The probe made it possible to measure the acidity in vivo, i.e., directly in the patient’s GIT. In the USSR, the first pH probes were developed by E. Yu. Linar and colleagues in 1950. They tested various designs, materials, and techniques for manufacture of pH probes. The works of Linar and Lei formed a basis for the development of domestic pH probes.

Until the beginning of the 1980s, equipment for intragastric pH monitoring (first-generation equipment) was designed mainly to substantiate the necessity of pH monitoring and develop new methods of medical examination. Both medical and technological results achieved at this time formed a basis for developing pH measuring equipment of the second generation. This equipment is intended for use in ordinary medical institutions. In the USSR, such devices were developed at the State Scientific-Manufacturing Company Istok-Sistema (Fryazino) under the supervision of Academician N. D. Devyatkov. Corresponding Member of the Russian Academy of Medical Sciences Yu. M. Pantsyrev and Professor S. A. Chernyakevich also contributed considerably to the development of such equipment. In the mid 1980s, serial manufacture of the intraoperation acidogastrometer AGMI-01 was arranged in Fryazino. The AGMI-01 acidogastrometer has a digital display indicating the current value of acidity in pH units (obtained data are corrected automatically according to the type of pH probe and the results of calibration). Despite its simplicity, the AGMI-01 acidogastrometer proved to be very efficient. It is still used in some medical institutions for direct short-term intraendoscopic and intraoperation pH monitoring. Simultaneously, the group headed by Devyatkov and Pantsyrev developed a number of pH probes with calomel reference electrodes, measuring antimonial electrodes, and medical rubber covers.

A small number of devices for intragastric pH monitoring produced by Synectics Gastro AB (Sweden), Albyn Medical Ltd. (Great Britain), and MMS (Netherlands) are presently used in domestic medical institutions. All these devices provide long-term monitoring of the GIT acidity. In addition to pH monitoring, some of them provide measurement of the intraesophageal pressure, the bile content, and the electrical activity of the GIT organs. Upon completion of the examination, the results of measurement are transmitted to a computer for processing. The main disadvantages of these devices are high cost, foreign language software and documentation, low availability of expendable materials, etc. Besides, these devices do not implement some measuring techniques conventionally used in domestic medical practice. On the other hand, inexpensive devices for short-term stimulated and intraendoscopic pH monitoring and screening examination of several patients are not available from foreign manufacturers.

Clinical Application of Intracavitary pH Monitoring

Development of pH measuring devices and probes gave rise to new clinical methods for examination of

acid-dependent processes in the human body. In modern medicine, intracavitary pH monitoring has the following applications.

Diagnostic applications:

– direct measurement of acidity at different sites of the GIT;

– short-term (up to 3 h) monitoring of the basal and stimulated secretion in the upper segments of the GIT;

– investigation of fast acid processes, such as duodenogastric refluxes;

– parietal intraendoscopic pH monitoring;

– long-term monitoring of acidity in the esophagus for the purpose of studying the role of the GER in bronchopulmonary and otorhinolaryngological diseases: chronic cough, pneumonia, bronchial asthma, sinusitis, dysphonia, laryngitis, bronchial obstruction, contact granuloma, pharyngitis, dental erosion; malignant diseases of the throat, larynx, and vocal cords; and sleep disorders;

– simultaneous long-term monitoring of the acidity in the upper segments of the GIT and the electrical activity of the heart for the purpose of differential diagnosis of cardiac and gastric diseases and investigation of GER-induced cardiac diseases; simultaneous monitoring of the acidity in the upper segments of the GIT and the electrical activity of various segments of the GIT.

Assessment of the effect of various drugs:

– selection and dosage of drugs for optimal medicinal treatment;

– assessment of the efficacy of drugs for treatment of various diseases;

– certification testing of drugs.

Devices for intracavitary pH monitoring can be effectively used for various research purposes, such as development and testing of new methods of diagnosis and treatment of the diseases of the upper segments of the GIT, investigation of the acid-dependent processes in the lower segments of the GIT and the oral cavity, and intravaginal and transurethral pH monitoring.

Devices for Intragastric pH Monitoring Available from State Scientific-Manufacturing Company Istok-Sistema

State Scientific-Manufacturing Company Istok-Sistema is the leading domestic manufacturer of devices and probes for intragastric (intracavitary) pH monitoring. It was founded 10 years ago as a branch of the State Scientific-Manufacturing Company Istok, one of the leading enterprises of the defense industry. First, Istok-Sistema Company specialized in manufacture of the acidogastrometers and pH probes developed by the Istok Company; then, it began to develop original devices for pH monitoring. At present, four basic devices in various modifications are available from Istok-Sistema Company. The production of Istok-Sistema Company satisfies the basic needs of the domestic medical institutions for equipment for intracavitary pH monitoring. Many leading clinics and ordinary medical institutions have been equipped with acidogastrometers, acidogastromonitors, and pH probes manufactured by the Istok-Sistema Company. This led to development of new clinical methods and upgrading of requirements for pH monitoring equipment. To meet these requirements, the Istok-Sistema Company developed a new improved family of pH measuring devices and probes. The main devices constituting this family are described below.

1. AGM-03 (AGM-MP-03-1) microprocessor acidogastrometer (Fig. 1). The AGM-03 acidogastrometer is used for measuring basal and stimulated acidity in the GIT; performing acid, alkaline, and other tests; selecting optimum drug therapy. In addition, it can be used for topographical intraendoscopic pH monitoring. The AGM-03 acidogastrometer is based on modern microprocessor technology. An advanced system of menus and prompts displayed on the indicator is very useful in performing medical examination of the GIT. A series of inexpensive acidogastrometers was developed based on the AGM-03 device.

Fig. 1. AGM-03 microprocessor acidogastrometer

2. Gastroskan-5M(AGM-05K) computer-assisted stationary acidogastrometer (Fig. 2). The Gastroskan-5M acidogastrometer is used for short-term (optionally stimulated) pH monitoring in the upper (1, 2, 3, or 5th) segments of the GIT in up to 5 patients simultaneously. The period of pH measurement is 20 or 5 sec. A system of prompts facilitates the examination. Upon measurement, the device forms a conclusion about the state of the upper segments of the GIT. The results of examination are stored in a database. The device provides various procedures for statistical treatment of the data obtained and makes it possible to select the optimal medicinal treatment with antacid preparations.

Fig. 2. Gastroskan-5M computer-assisted stationary acidogastrometer

3. Gastroskan-24 (AGM-24MP) portable acidogastrometer (Fig. 3). The Gastroskan-24 acidogastrometer is used for long-term (24 h and more) monitoring of the acidity in the upper segments of the GIT. Measurements are performed using a transnasal pH probe and an autonomous portable recording unit. Upon completion of measurement, the obtained data are transmitted to a computer for processing. The device makes it possible to assess the effect of various drugs and select the optimal mode of medicinal treatment.

Fig. 3. Gastroskan-24 portable acidogastrometer

During examination, the patient enters the information about the state of his/her health (pain, heartburn, nausea, etc.) and other factors (smoking, current medicinal treatment, etc.) from the keyboard of the portable unit. This information and the results of measurement of acidity in three segments of the GIT are stored in the RAM of the device. The results of measurement can be indicated in online mode on the liquid-crystal display of the portable unit or (upon transmission to the computer) on the computer monitor.

4. Gastroskan-EKG (GKM-01) gastrocardiomonitor (Fig. 4). The Gastroskan-EKG device consists of a portable recording unit carried by the patient for 24 h, a pH probe, with two measuring and one reference electrode, a set of electrodes for 24-h monitoring of the bioelectric cardiac potentials (ECG), computer, software for analysis and processing of the results of measurement, storage database, connecting and calibration cables, and a device for calibration of pH probes.

Fig. 4. Gastroskan-EKG gastrocardiomonitor

The Gastroenterology database is used in all computer-assisted devices manufactured by the Istok-Sistema Company. It includes the following main units:

– patient information;

– examination;

– visualization of the results of examination and their output to printer;

The design of a pH probe is determined mainly by the its clinical application and the requirements for the patient’s safety. The cost factor is also taken into consideration. In foreign medicine, expendable and semiexpendable (for 3-5 examinations) probes are widely used. However, use of expendable electrodes is too expensive for some domestic medical institutions. pH probes can be classified according to the regions of their application into the following groups: a) intra-gastric; b) anorectal; c) intravaginal; and d) maxillo-facial.

Intragastric probes are applied perorally, transnasally, or intraendoscopically. Peroral and transnasal probes can from one to five measuring electrodes (three-electrode probes are especially widely used). Transnasal probes are mainly used for 24-h examinations; peroral probes are usually used for shorter examinations. Peroral and transnasal probes differ in the diameter of the tube. Intraendoscopic probes have a single measuring electrode; their diameter should match the diameter of the instrumental channel of the endoscope. Multielectrode pH probes differ in the distance between the measuring electrodes (adjusted according to the patient’s age). Five modifications of multielectrode pH probes for examination of patients of various age (four for examination of children and one for adults) have been adopted by the Ministry of Health of the Russian Federation.

Probes for pH monitoring have antimony or glass measuring electrodes. The glass electrodes provide better accuracy of measurement, but they have several disadvantages: fragility, high input resistance, high cost, etc. Besides, the pores on their surface are easily clogged.

That is why glass electrodes have not found wide application for intragastric pH monitoring. According to the design and technology of manufacture of the reference electrodes, pH probes can be classified into the following groups: probes with an external cutaneous silver chloride reference electrode and probes with an internal silver chloride reference electrode.

Many years of experience in manufacture and use of pH probes showed that it is optimal to use polyvinylchloride probes with a cutaneous silver chloride reference electrode and one or several (up to 5) measuring antimony electrodes implemented as cylindrical rings or columns and mounted on a polyvinylchloride or fluoroplastic tube. The main types of pH probes commercially available from Istok-Sistema are listed below.

Peroral probes have 2, 3, or 5 measuring electrodes. They are available in 5 modifications for examination of patients of different ages and are used for direct short-term pH monitoring. Their outer diameter is 4.2 mm.

Transnasal probes have 3 measuring electrodes and are available in 5 modifications for examination of patients of different ages. They are used for long-term monitoring. Their outer diameter is 2.2 mm.

Endoscopic probes have one measuring electrode. They are used for parietal topographic pH monitoring during endoscopic examination. The outer diameter is determined by the diameter of the instrumental channel of the endoscope (1.8 or 2.4 mm).

All pH probes provide a measurement accuracy of 0.2 pH in the range from pH 1.1 to 9.2.

Biomedical research often requires custom-made pH probes. For example, investigation of the role of the GER in bronchopulmonary or otorhinolaryngological diseases requires pH probes with nonstandard arrangement of measuring electrodes. Intravaginal pH monitoring or investigation of the acid-dependent processes in the oral cavity require the standard design of pH probes to be modified according to the morphology of the organ under examination.

Conclusion

Domestic devices and probes for intracavitary pH monitoring compete successfully with the production of foreign manufacturers on the market of the former Soviet Union. During the period of economic reforms in Russia, the annual sales of foreign acidogastrometers on the domestic market have never exceeded 5% in money terms (0.5% in real terms) from the total annual sales. The acidogastrometers, acidogastromonitors, and pH probes manufactured by the Istok-Sistema Company are successfully used in the gastroenterological departments of the largest medical institutions of the Russian Federation. Intracavitary pH monitoring is an essential part of modern gastroenterology of the upper segments of the GIT. It also begins to be used in pulmonology, cardiology, and other branches of medicine.